Blow an alarm - i. e. along continuous peal. Compare Numbers 10:7, ye shall blow, but not sound an alarm: i. e. blow in short, sharp notes, not in a continuous peal. A third and a fourth alarm were probably blown as signals.

When ye blow an alarm - תרועה teruah, probably meaning short, broken, sharp tones, terminating with long ones, blown with both the trumpets at once. From the similarity in the words some suppose that the Hebrew teruah was similar to the Roman taratantara, or sound of their clarion.

When ye blow an alarm, then the camps that lie on the (b) east parts shall go forward.
(b) That is, the host of Judah and they that are under his ensign.

When ye blow an alarm,.... Making a broken, uneven, and quavering sound, which is called a "tara-tan-tara":
then the camps that lie on the east parts shall go forward; the camps of Judah, Issachar, and Zebulun, which lay to the east of the tabernacle, at the front of it; see Numbers 1:3; this was to be the token for their march, which was first of all; Numbers 10:14.

To give the signal for breaking up the camp, they were to blow תּרוּעה, i.e., a noise or alarm. At the first blast the tribes on the east, i.e., those who were encamped in the front of the tabernacle, were to break up; at the second, those who were encamped on the south; and so on in the order prescribed in ch. 2, though this is not expressly mentioned here. The alarm was to be blown למסּעיהם, with regard to their breaking up or marching.